You will be blamed.
Making mistakes and regrets after following your dreams is crucial. And if it happens, people will start blaming you instead of encouraging and helping you not to give up in aiming for your dreams.
You will disappoint yourself.
Dreaming might come to reality, but most only remain as dreams. That is because you could be dreaming a very unrealistic thing. You will then end up being disappointed after everything you thought of as possible only fails you.